Little to no heat upstairs

I have a hot water boiler system in my house. Overall the house is nice and warm. Upstairs Bedroom 1 has a nice big old cast radiator with a line coming pretty much straight up from the boiler to feed it. That room is fine. The rooms that are not warm are highlighted in dark blue. They all have convectors (two are only one year old). They just don't seem to warm up. The system is only one zone, and I'm thinking that is the problem. Last night I cranked the temp up to 73 and it was warmer upstairs, but the convectors still didn't seem that warm. So I went and checked the lines coming upstairs (in attic space). The line coming up was hot, but the return was barely warm.

Any suggestions/observations based on my drawing of the system? Just trying to see what I'm looking at here and what options we might have.

I have bled the radiator in Upstairs Room 1. I'm not sure how you bleed the convectors in the other rooms. There is a drain on both the supply and return sides of that loop upstairs, could I do it from the return side drain?

Your diagram is just a logical representation of the system. Not knowing your acutal piping and valve arrangement makes it a bit difficult to point you in the right direction. Is your system a 1 pipe, 2 pipe? Would help if you could give us some more piping lines that represent supply and returns. Pics would also help greatly.

If you don't have a way to bleed at the actual convectors then yes you will most likely need to purge the air from some drains down in the basement. Depending on your valve arrangement this may be very easy or a bit more of a pain.

The diagram is accurate as far as how the water flows out of the boiler and where it splits etc. I could label each of the lines with what type/size pipe is in there. The drains I'm talking about are actually in the kneewall attic upstairs so I can see what I can get out of those today and see if it makes a difference in the return temp. The convector in the bathroom upstairs has a little handle "valve" type thing on it. If I turn it it seems to just move freely. I wonder if there is something up at that point that is restricting the water flow past it?

The diagram is accurate as far as how the water flows out of the boiler and where it splits etc. I could label each of the lines with what type/size pipe is in there. The drains I'm talking about are actually in the kneewall attic upstairs so I can see what I can get out of those today and see if it makes a difference in the return temp. The convector in the bathroom upstairs has a little handle "valve" type thing on it. If I turn it it seems to just move freely. I wonder if there is something up at that point that is restricting the water flow past it?

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The diagram doesn't show how the water gets back to the boiler? Also are you sure that the bathroom and bed 2 and 3 loop from on to the next? That would mean that after bed#3 there would have to be a line coming back to the boiler. You can determine where the airlock is by seeing where the heat stops.

By your diagram it gets to the bathroom, if you have no heat at that unit then there is air from that point forward. If you have no bleeders on any of those 3 units then you need to drain from a drain after bedroom 3. The problem is that if you open that drain the water needs to go from

boiler--->bathroom---->bedroom2---->bedroom3------>drain--->return to boiler.

if you open the drain and don't have a way to isolate the boiler then the water that comes out of the drain will be coming up from the boiler and not thru the bed 3 convector. Follow?

Yeah I didn't put the return on the diagram, sorry about that. Right where the water comes upstairs there are shutoffs on both the feed and return that feed the problem area. That's where the drains are also. I see what you mean about the bed 3 convector. Let me go up into the attic and see how that flows and I'll draw up a diagram of just the upstairs portion since thats the issue.

Since you say there are shutoffs and drains down there it sounds like someone plumbed it correctly.

I'm going to assume the shutoff on the return is between the drain and boiler. If thats the case then you simply close that shutoff. and open the drain valve. I usually connect a washing machine hose to the drain valve and drain into a bucket.

This will make water flow up the supply side and thru the convectors pushing all the air out of the open drain. It will spurt and sputter. When the water runs steady with no air you can close the drain and open the shutoff valve.

My process whenever I'm working on one of my loops is to flip the switch on the boiler so no burner or pumps will run. Then I close off any other loops that have valves so as to not introduce air into those other loops. Then I flip the feed on my auto feed to fast fill the system with water while I'm purging air on the loop i'm working on.

Ok, I put a small hose on the drain, shut off the return to the boiler and opened the drain, it took a few seconds for water to come out and then I let it run until the bucket was full, shut the drain off, opened up the return and dumped the bucket. I guess I'll see if that makes a difference, but at least I know water is going through the whole loop upstairs for sure now, and not being blocked in the bathroom right away.

The stat was set low when I did this, so I turned it up and waited a bit. When I checked both pipes in my bedroom (upstairs bedroom 3) were hot. When I get home later tonight I'm going to check the return in the attic and see if it's now hot.